Diamide-induced alterations of intracellular thiol status and the regulation of glucose metabolism in the developing rat conceptus in vitro

Redox processes are major regulators of leukotriene synthesis in neutrophils exposed to bacteria Salmonella typhimurium; the way to manipulate neutrophil swarming

Neutrophils play a primary role in protecting our body from pathogens. When confronted with invading bacteria, neutrophils begin to produce leukotriene B4, a potent chemoattractant that, in cooperation with the primary bacterial chemoattractant fMLP, stimulates the formation of swarms of neutrophils surrounding pathogens. Here we describe a complex redox regulation that either stimulates or inhibits fMLP-induced leukotriene synthesis in an experimental model of neutrophils interacting with Salmonella typhimurium. The scavenging of mitochondrial reactive oxygen species by mitochondria-targeted antioxidants MitoQ and SkQ1, as well as inhibition of their production by mitochondrial inhibitors, inhibit the synthesis of leukotrienes regardless of the cessation of oxidative phosphorylation. On the contrary, antioxidants N-acetylcysteine and sodium hydrosulfide promoting reductive shift in the reversible thiol-disulfide system stimulate the synthesis of leukotrienes. Diamide that oxidizes glutathione at high concentrations inhibits leukotriene synthesis, and the glutathione precursor S-adenosyl-L-methionine prevents this inhibition. Diamide-dependent inhibition is also prevented by diphenyleneiodonium, presumably through inhibition of NADPH oxidase and NADPH accumulation. Thus, during bacterial infection, maintaining the reduced state of glutathione in neutrophils plays a decisive role in the synthesis of leukotriene B4. Suppression of excess leukotriene synthesis is an effective strategy for treating various inflammatory pathologies. Our data suggest that the use of mitochondria-targeted antioxidants may be promising for this purpose, whereas known thiol-based antioxidants, such as N-acetylcysteine, may dangerously stimulate leukotriene synthesis by neutrophils during severe pathogenic infection.

Discovery of a Redox Thiol Switch: Implications for Cellular Energy Metabolism

The redox-based modifications of cysteine residues in proteins regulate their function in many biological processes. The gas molecule H2S has been shown to persulfidate redox sensitive cysteine residues resulting in an H2S-modified proteome known as the sulfhydrome. Tandem Mass Tags (TMT) multiplexing strategies for large-scale proteomic analyses have become increasingly prevalent in detecting cysteine modifications. Here we developed a TMT-based proteomics approach for selectively trapping and tagging cysteine persulfides in the cellular proteomes. We revealed the natural protein sulfhydrome of two human cell lines, and identified insulin as a novel substrate in pancreatic beta cells. Moreover, we showed that under oxidative stress conditions, increased H2S can target enzymes involved in energy metabolism by switching specific cysteine modifications to persulfides. Specifically, we discovered a Redox Thiol Switch, from protein S-glutathioinylation to S-persulfidation (RTSGS). We propose that the RTSGS from S-glutathioinylation to S-persulfidation is a potential mechanism to fine tune cellular energy metabolism in response to different levels of oxidative stress.

Glutathione during embryonic development

BACKGROUND

Glutathione (GSH) is a ubiquitous, non-protein biothiol in cells. It plays a variety of roles in detoxification, redox regulation and cellular signaling. Many processes that can be regulated through GSH are critical to developing systems and include cellular proliferation, differentiation and apoptosis. Understanding how GSH functions in these aspects can provide insight into how GSH regulates development and how during periods of GSH imbalance how these processes are perturbed to cause malformation, behavioral deficits or embryonic death.

SCOPE OF REVIEW

Here, we review the GSH system as it relates to events critical for normal embryonic development and differentiation.

MAJOR CONCLUSIONS

This review demonstrates the roles of GSH extend beyond its role as an antioxidant but rather GSH acts as a mediator of numerous processes through its ability to undergo reversible oxidation with cysteine residues in various protein targets. Shifts in GSH redox potential cause an increase in S-glutathionylation of proteins to change their activity. As such, redox potential shifts can act to modify protein function on a possible longer term basis. A broad group of targets such as kinases, phosphatases and transcription factors, all critical to developmental signaling, is discussed.

GENERAL SIGNIFICANCE

Glutathione regulation of redox-sensitive events is an overlying theme during embryonic development and cellular differentiation. Various stresses can change GSH redox states, we strive to determine developmental stages of redox sensitivity where insults may have the most impactful damaging effect. In turn, this will allow for better therapeutic interventions and preservation of normal developmental signaling. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Dietary supplemented 2-mercaptoethanol prevents spontaneous and delays virally-induced murine mammary tumorigenesis

There seems to be little doubt that organosulfur compounds have enormous benefits for biological processes, especially those of diseases like cancer. The preliminary results herein define a cancer model in which benefits/mechanisms of multitudes of xenobiotic and nature's organosulfurs could easily be compared. Mice from three strains with a high incidence for naturally occurring tumors were treated daily with 2-mercaptoethanol (2-Me) starting at weaning. The 100% tumor incidence of undefined etiology in untreated BXSB-Yaa (+) males was completely prevented by 2-Me. In contrast, 2-Me treatment of female and male C3H.OL and C3H.OH congenic strains, did not change the 100% tumor incidence due to milk-borne retrovirus, MMTV(S), but did: (1) delay the appearance of tumors by 42%; (2) increase longevity 56%; and (3) increase longevity, post-tumor detection, 95%. The addition of these results to the increasingly impressive anti-cancer benefits of simple xenobiotic organosulfurs raise the question: Can they be adapted for use as a preventive modality for human cancer?

Anticancer activity and chemoprevention of xenobiotic organosulfurs in preclinical model systems

There seems to be little doubt that xenobiotic and plant derived organosulfur compounds have enormous benefits for in vitro cellular functions and for a multitude of diseases, including cancer. Since there are numerous reviews on anticancer activities of plant organosulfurs, the focus herein will be on alterations associated with xenobiotic organosulfurs. Benefits of 2-mercaptoethanol (2-Me), N-Acetyl-cysteine, cysteamine, thioproline, piroxicam, disulfiram, amifostine, sulindac, celecoxib, oltipraz and their derivates on transplanted homologous tumors and on autochthonous cancers with a viral-, radiation-, chemical carcinogen-, and undefined-etiology are assessed. Because all organosulfurs were not tested for activity in each of the etiology categories, comparative evaluations are restricted. In general, all ‘appeared’ to lower the incidence of cancer irrespective of etiology; however, since most of these values were determined at ages much younger than at a natural-end-of-life-age, differences most likely, instead, reflect a delayed initiation and/or a slowed progression of tumorigenesis. The poorest, long-term benefits of early intervention protocols occurred for viral- and chemical carcinogen-induced cancers. In addition, once tumorigenesis was beyond the initiation stage, outcomes of organosulfur therapies were extremely poor, indicating that they will not be of significant value as stand alone treatments. More importantly, except for the lifetime prevention of spontaneous and radiation-induced mammary tumors by daily dietary 2-Me, similar life long prevention of tumorigenesis was not achieved with other xenobiotics or any of nature’s plant organosulfurs. These results raise an interesting question: Is the variability in incidence found for different organosulfurs associated with (a) their structure, (b) the length of the untreated latency period, (c) treatment duration/dose, and/or (d) the etiology-inducing agent?

New insights into redox response modulation in Fanconi's anemia cells by hydrogen peroxide and glutathione depletors

Fanconi's anemia (FA) patients face severe pathological consequences. Bone marrow failure, the major cause of death in FA, accounting for as much as 80-90% of FA mortality, appears to be significantly linked to excessive apoptosis of hematopoietic cells induced by oxidative stress. However, 20-25% of FA patients develop malignancies of myeloid origin. A survival strategy for bone marrow and hematopoietic cells under selective pressure evidently exists. This study reports that lymphoblastoid cell lines derived from two FA patients displayed significant resistance to oxidative stress induced by treatments with H(2) O(2) and various glutathione (GSH) inhibitors that induce production of reactive oxygen species, GSH depletion and mitochondrial membrane depolarization. Among the various GSH inhibitors employed, FA cells appear particularly resistant to menadione (5 μm) and ethacrynic acid (ETA, 50 μm), two drugs that specifically target mitochondria. Even after pre-treatment with buthionine sulfoximine, a GSH synthesis inhibitor that induces enhanced induction of reactive oxygen species, FA cells maintain significant resistance to these drugs. These data suggest that the resistance to oxidative stress and the altered mitochondrial and metabolic functionality found in the FA mutant cells used in this study may indicate the survival strategy that is adopted in FA cells undergoing transformation. The study of redox and mitochondria regulation in FA may be of assistance in diagnosis of the disease and in the care of patients.

Glutathione homeostasis and functions: potential targets for medical interventions

Glutathione (GSH) is a tripeptide, which has many biological roles including protection against reactive oxygen and nitrogen species. The primary goal of this paper is to characterize the principal mechanisms of the protective role of GSH against reactive species and electrophiles. The ancillary goals are to provide up-to-date knowledge of GSH biosynthesis, hydrolysis, and utilization; intracellular compartmentalization and interorgan transfer; elimination of endogenously produced toxicants; involvement in metal homeostasis; glutathione-related enzymes and their regulation; glutathionylation of sulfhydryls. Individual sections are devoted to the relationships between GSH homeostasis and pathologies as well as to developed research tools and pharmacological approaches to manipulating GSH levels. Special attention is paid to compounds mainly of a natural origin (phytochemicals) which affect GSH-related processes. The paper provides starting points for development of novel tools and provides a hypothesis for investigation of the physiology and biochemistry of glutathione with a focus on human and animal health.

Gender-specific proteomic responses in zebrafish liver following exposure to a selected mixture of brominated flame retardants

Proteomic effect screening in zebrafish liver was performed to generate hypotheses following exposure (21 days) to a structurally diverse mixture of brominated flame retardants (BFRs). Fish were exposed to two doses (10 and 100 nmol/g feed). Two-dimensional gel-electrophoresis, image analysis and MALDI-TOF mass-spectrometry revealed 13 and 19 significant responses in males and females, respectively. Effects on proteins related to cellular maintenance and stress were observed in both genders. Regulated proteins were gender-specific, but functionally indicated common protective responses (peroxiredoxin 6 and Zgc:92891 in males and transketolase in females) suggesting oxidative stress. Betaine homocysteine methyltransferase (BHMT) was induced in both genders. In addition a female-specific downregulation of ironhomeostatic proteins (iron-regulatory protein 1 and transferrin) were observed. Our proteomic approach revealed novel responses that suggest important gender-specific sensitivity to BFRs that should be considered when interpreting adverse effects of BFRs.

Activator protein-1 (AP-1) DNA binding activity is induced by hydroxyurea in organogenesis stage mouse embryos

Hydroxyurea is a potent teratogen; free radical scavengers or antioxidants reduce its teratogenicity. Activator Protein-1 (AP-1) and NF-kappaB are redox-sensitive transcription factors with important roles in normal development and the stress response. This study was designed to determine if exposure to teratogenic doses of hydroxyurea induces oxidative stress and alters gene expression by activating these transcription factors. Pregnant mice were treated with saline or hydroxyurea (400, 500, or 600 mg/kg) on gestation day 9 (GD 9) and killed either on GD 9, 0.5, 3, or 6 h after treatment, to assess oxidative stress and transcription factor activities, or on GD 18, to assess fetal development. Exposure to 400 mg/kg hydroxyurea did not affect the progeny, whereas exposure to 500 or 600 mg/kg resulted in dose-dependent increases in fetal resorptions and malformations, including curly tails, abnormal limbs (oligodactyly, hemimelia, and amelia), and short ribs. Hydroxyurea did not induce oxidative stress, as assessed by the ratio of oxidized to reduced glutathione, nor did it alter NF-kappaB DNA binding activity in the GD 9 conceptus. In contrast, exposure to hydroxyurea at any dose increased AP-1 DNA binding activity in embryos and yolk sacs 0.5 or 3 h after treatment. Hydroxyurea-induced c-Fos heterodimer activity in the embryo peaked 3-4-fold above control at 3 h and remained elevated by 6 h; in contrast, the activity of c-Jun dimers was not altered by drug exposure. A dramatic and region-specific increase in c-Fos immunoreactivity was found in hydroxyurea-treated embryos. The induction of AP-1 DNA binding activity by hydroxyurea represents an early, sensitive marker of the embryonic response to insult.

Addition of β-mercaptoethanol or Trolox® at the morula/blastocyst stage improves the quality of bovine blastocysts and prevents induction of apoptosis and degeneration by prooxidant agents

This study was conducted to evaluate the effect of beta-mercaptoethanol (a stimulator of glutathione synthesis) and Trolox (an hydrosoluble analogue of Vitamin E) on bovine embryos cultured from the morula stage (Day 5 post-insemination; pi) under oxidative stress conditions. Culture of embryos with increased doses of Trolox showed a dose-dependent embryotoxicity on Day 8 pi. The use of 400 microM Trolox as well as beta-mercaptoethanol at 100 microM prevented at least partly (P < 0.05) the prooxidant-induced blastocyst degeneration on Day 8. Hatching rates of surviving blastocysts were significantly increased by both antioxidants and beta-mercaptoethanol alone improved their mean cell numbers, which was significant in the ICM (P < 0.05). Analysis of their effect on Day 7 pi showed that both the antioxidants significantly reduced the prooxidant-induced apoptosis and beta-mercaptoethanol diminished the physiological level of apoptosis as well as it stimulated the glutathione synthesis (P < 0.05). In addition, a comparison between in vitro- and in vivo-produced embryos showed that the levels of apoptosis were similar at the same age post-insemination (morulae and blastocysts) but increased steadily with the embryonic age in in vitro ones. In conclusion, beta-mercaptoethanol and Trolox added separately from the morula stage protected embryos against oxidative stress and improved the quality of the resulting blastocysts.

Maternal diabetes in vivo and high glucose in vitro diminish GAPDH activity in rat embryos

The aim of the present study was to investigate whether diabetic embryopathy may be associated with the inhibition of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) resulting from an excess of reactive oxygen species (ROS) in the embryo. Recent demonstrations of enhanced ROS production in mitochondria of bovine aortic endothelial cells exposed to high glucose have supported the idea that the pathogenesis of diabetic complications may involve ROS-induced GAPDH inhibition. We investigated whether a teratogenic diabetic environment also inhibits embryonic GAPDH activity and alters GAPDH gene expression and whether antioxidants diminish such GAPDH inhibition. In addition, we determined whether the inhibition of GAPDH with iodoacetate induces dysmorphogenesis, analogous to that caused by high glucose concentration, and whether antioxidants modulated the putative teratogenic effect of such direct GAPDH inhibition. We found that embryos from diabetic rats and embryos cultured in high glucose concentrations showed decreased activity of GAPDH (by 40-60%) and severe dysmorphogenesis on gestational days 10.5 and 11.5. GAPDH mRNA was decreased in embryos of diabetic rats compared to control embryos. Supplementing the high-glucose culture with the antioxidant N-acetylcysteine (NAC) increased GAPDH activity and diminished embryonic dysmorphogenesis. Embryos cultured with iodoacetate showed both decreased GAPDH activity and dysmorphogenesis; supplementing the culture with NAC increased both parameters toward normal values. In conclusion, dysmorphogenesis caused by maternal diabetes is correlated with ROS-induced inhibition of GAPDH in embryos, which could indicate that inhibition of GAPDH plays a causal role in diabetic embryopathy.

Spatial glutathione and cysteine distribution and chemical modulation in the early organogenesis-stage rat conceptus in utero

Glutathione (GSH), cysteine, and other low-molecular-weight thiols (LMWT) play a vital role in the detoxication of xenobiotics and endogenous chemicals. Differential alterations of LMWT status in various cell types of the developing embryo may underlie cell-specific sensitivity or resistance to xenobiotics and contribute to embryotoxicity. This study describes the spatial and temporal distribution of LMWTs in rat conceptuses and alterations produced by the non-teratogenic GSH modulator, acetaminophen (APAP). Pregnant female rats were given 125, 250, or 500 mg/kg APAP (po) on gestational day 9. Conceptal LMWT was localized histochemically using mercury orange in cryosections, and GSH and cysteine concentrations were measured by HPLC analysis. Mercury orange histofluorescence revealed a non-uniform distribution of LMWT in untreated conceptal tissues, with strongest staining observed in the ectoplacental cone (EPC), visceral yolk sac (VYS), and embryonic heart. Less intense staining was observed in the neuroepithelium. Following treatment with APAP, tissue-associated LMWT decreased dramatically except in the EPC, while exocoelomic fluid LMWT, and LMWT within embryonic lumens, increased. Exposure to 250 mg/kg APAP decreased embryonic GSH after 6 and 24 h by 46% and 38%, respectively. Acetaminophen (500 mg/kg) decreased embryonic and VYS cysteine content by 54% and 83%, respectively, after 24 h. Acetaminophen alters the spatial distribution of LMWT in rat conceptuses, particularly with respect to cysteine. The mobilization of cysteine following chemical insult may influence the ability of conceptal cells to maintain normal GSH status due to reduced availability of cysteine for de novo GSH synthesis.

Developmental ontogeny of NAD+ kinase in the rat conceptus

The ubiquitous NAD+ kinase (NADK) is the only known enzyme to catalyze formation of NADP+ from NAD+. The capacity to maintain an adequate supply of NADP(H) has important implications for development because of its requirement as a cofactor and electron donor in biosynthesis and detoxication reactions. Modulation of NADK may directly influence NADP(H) concentrations and cell sensitivity to embryotoxicants. Measurable activities of NADK were not detected in gestational day (GD) 10 rat conceptuses. By GD 11, specific activities of 1.8 and 7.0 pmol NADP+/min/microg protein were measured in embryos and visceral yolk sacs (VYSs), respectively. The VYS specific activities decreased thereafter to 0.5 pmol NADP+/min/microg protein by GD 18. Specific activities of NADK in placenta increased from 1.3 pmol NADP+/min/microg protein on GD 11 to 32.7 pmol NADP+/min/microg protein on GD 15. Specific activities in the liver increased from 1.7 pmol NADP+/min/microg protein on GD 15 to 51.1 pmol NADP+/min/microg protein on GD 21. NADK specific activities were also determined in other developmentally relevant tissues such as the heart and the brain. In the heart, NADK activity was at its lowest just before birth while in the brain it peaked at 5.4 pmol NADP+/min/microg protein just prior to birth. In the lung, activity increased from 0.9 pmol NADP+/min/microg protein on GD 17 to 5.9 pmol NADP+/min/microg protein on GD 21. However, activities dropped in the kidney from 2.0 pmol NADP+/min/microg protein on GD 17 to 1.1 pmol NADP+/min/microg protein on GD 21. These results demonstrate dramatic temporal and spatial variations in NADK activity. Tissue variations in NADK activities may reflect alterations in functional needs for cofactors during differentiation and a cooperation between tissues to optimize detoxification capacity. This is particularly important when chemical exposure during pregnancy disrupts pyridine nucleotide redox status and the conceptus must rely on NADK to provide additional NADP(H).

Oxidative damage in chemical teratogenesis

The teratogenicity of many xenobiotics is thought to depend at least in part upon their bioactivation by embryonic cytochromes P450, prostaglandin H synthase (PHS) and lipoxygenases (LPOs) to electrophilic and/or free radical reactive intermediates that covalently bind to or oxidize cellular macromolecules such as DNA, protein and lipid, resulting in in utero death or teratogenesis. Using as models the tobacco carcinogens benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), the anticonvulsant drug phenytoin, structurally related anticonvulsants (e.g. mephenytoin, nirvanol, trimethadione, dimethadione) and the sedative drug thalidomide, we have examined the potential teratologic relevance of free radical-initiated, reactive oxygen species (ROS)-mediated oxidative molecular target damage, genotoxicity (micronucleus formation) and DNA repair in mouse and rabbit models in vivo and in embryo culture, and in vitro using purified enzymes or cultured rat skin fibroblasts. These teratogens were bioactivated by PHS and LPOs to free radical reactive intermediary metabolites, characterized by electron spin resonance spectrometry, that initiated ROS formation, including hydroxyl radicals, which were characterized by salicylate hydroxylation. ROS-initiated oxidation of DNA (8-hydroxy-2'-deoxyguanosine formation), protein (carbonyl formation), glutathione (GSH) and lipid (peroxidation), and embryotoxicity were shown for phenytoin, its major hydroxylated metabolite 5-(p-hydroxyphenyl)-5-phenylhydantoin [HPPH], thalidomide, B[a]P and NNK in vivo and/or in embryo culture, the latter indicating a teratologically critical role for embryonic, as distinct from maternal, processes. DNA oxidation and teratogenicity of phenytoin and thalidomide were reduced by PHS inhibitors. Oxidative macromolecular lesions and teratogenicity also were reduced by the free radical trapping agent phenylbutylnitrone (PBN), and the antioxidants caffeic acid and vitamin E. In embryo culture, addition of superoxide dismutase (SOD) to the medium enhanced embryonic SOD activity, and SOD or catalase blocked the oxidative lesions and embryotoxicity initiated by phenytoin and B[a]P, suggesting a major contribution of ROS, as distinct from covalent binding, to the teratologic mechanism. In in vivo studies, other antioxidative enzymes like GSH peroxidase, GSH reductase and glucose-6-phosphate dehydrogenase (G6PD) were similarly protective. Even untreated G6PD-deficient mice had enhanced embryopathies, indicating a teratological role for endogenous oxidative stress. In cultured fibroblasts, B[a]P, NNK, phenytoin and HPPH initiated DNA oxidation and micronucleus formation, which were inhibited by SOD. Oxidation of DNA may be particularly critical, since transgenic mice with +/- or -/- deficiencies in the p53 tumor suppressor gene, which facilitates DNA repair, are more susceptible to phenytoin and B[a]P teratogenicity. Even p53-deficient mice treated only with normal saline showed enhanced embryopathies, suggesting the teratological importance of endogenous oxidative stress, as observed with G6PD deficiency. These results suggest that oxidative macromolecular damage may play a role in the teratologic mechanism of xenobiotics that are bioactivated to a reactive intermediate, as well in the mechanism of embryopathies occurring in the absence of xenobiotic exposure.

Chemical teratogenesis in humans: biochemical and molecular mechanisms

In this review, an attempt has been made to summarize our current understanding of the mechanisms whereby certain chemicals cause birth defects. The chemicals selected for consideration were those that have been designated as established or recognized human teratogens. It is clear that our current understanding of mechanisms whereby these agents cause teratogenic effects (birth defects) can vary dramatically from one agent to the next. Extremes include the folic acid antagonists, which are now well established as agents that produce birth defects by virtue of potent inhibition of dihydrofolate reductase as a primary biochemical mechanism. An example at the other extreme is ethanol, for which very few definitive statements can be made with regard to teratogenic mechanisms, and the probability exists that a large number of interacting, contributory mechanisms can be invoked. For nearly all chemical teratogens, the critical links in the chains of events between the initial, primary biochemical and molecular mechanistic event (e.g. dihydrofolate reductase inhibition) and the manifestations of specific abnormalities (pathogenic mechanisms) remain to be delineated. This will provide an enormous challenge for investigators for years to come.